(a) Field of the Invention
For the DC brushless motor drive circuit with speed variable-voltage of the present invention, a closed loop drive circuit is formed, in which, under various running speeds statuses, the voltage supplied to the DC brushless motor is relatively increased or decreased on the basis of the internal setting of the motor drive control device according to the increased or decreased output rotational speed, so as to prevent the shortcoming of too much variation of the input impedance caused by the inductive reactance of the winding accordingly changed when the speed of the DC brushless motor is changed, specifically, to prevent the shortcoming of unable producing required torque resulting from the increased inductive reactance caused by increasing the rotational speed which makes the current value become too low when input by the original working voltage.
(b) Description of the Prior Art
The DC brushless motor is usually equipped with the electric machinery angle position detection unit, to detect the variation of the relative electric machinery angle position, during revolution, between the first electric machinery structure constituted by the magnetic field winding and the magnetic circuit, and the second electric machinery structure constituted by the permanent magnetic pole or the winding excitation type magnetic pole, in which the excitation sequence of the magnetic field winding or the excitation polarity of the magnetic field winding is switched by the motor drive control device, and the inductive reactance of the winding is accordingly increased or decreased with the fast or slow speed when the excitation sequence or the excitation polarity of the magnetic field winding is changed.
Therefore, the following shortcoming exists, when the DC voltage input to the DC brushless motor is higher, and the speed of the electric machinery is accordingly faster, if the driven load is increased, because the inductive reactance of the electric machinery is too high, the original input voltage is not enough to increase the input excitation current with the increased load, thus the drive torque is not enough.